(a) Technical Field
The present disclosure of invention relates to a display device. More particularly, the present invention relates to a display device including a backlighting unit and to a method of improving energy efficiency of providing backlighting.
(b) Description of Related Technology
Thin panel displays (e.g., flat panel or curved panel displays) may be categorized as self-lighting ones and externally illuminated ones. Examples of self-lighting ones include direct light emitting diode displays (LEDD's), electric field emission displays (EFED's), vacuum fluorescent displays (VFD's), and plasma display panels (PDP's). Examples of externally illuminated thin panel displays include reflective and/or transmissive liquid crystal displays (LCD's), electrically-displaceable dye displays (EDDD's) and electrophoretic displays (EPD's).
The externally illuminated thin panel displays may passively rely on ambient light or they may actively provide their own light for example form an attached backlighting unit (also referred to here as a light source unit). The light source unit may include one or more different types of light sources for generating its light. Examples of the light sources are a cold cathode fluorescent lamp (CCFL), a flat fluorescent lamp (FFL), and a light emitting diode (LED—colored and/or white). Recently, it has become desirable to use light emitting diodes (LED's) in a manner that reduces power consumption and generates less heat.
It is desirable for the backlight unit to provide uniform irradiation to a rear surface of the display panel. Backlighting units may be classified into edge illuminating types, direct backlighting types and hybrid types according to positionings of their respective light sources. The edge illuminating types typically employ a light guide plate (LGP) for redirecting edge-sourced light to be directed uniformly toward the back side of the to-be-backlit display panel.
The display panel includes a plurality of pixels, a plurality of switching elements for selectively driving the pixel electrodes and a plurality of signal lines for supplying control and data signals. The signal lines typically include a plurality of spaced apart gate lines extending in a first lateral direction for transmitting corresponding gate signals to respective rows of switching elements and a plurality of data lines extending in a different second lateral direction for transmitting respective data signals to corresponding columns of switching elements. At least one switching element in each pixel unit is connected to an adjacent gate line and to an adjacent data line for thereby receiving corresponding gate and data voltages.
In more detail, the typical display panel includes controlled light transmission regions (aperture regions) through which light is controllably transmitted, and light blocking regions through which transmission of light is undesirable because light in those regions cannot be appropriately controlled to form a desired image. Accordingly, when light is uniformly emitted from a backlighting unit to a display panel that has light blocking regions, the portions of the output light that fall on the light blocking regions are not transmitted through to form an image and their energy is lost (wasted).
The signal lines of the display panel are typically made of conductive metals, and light may be reflected from lower surfaces of such signal line so as to be reflected back the backlight unit for reuse and attempted transmission through the transmission regions of the display panel. However, when an attempt is made to reuse light in such manner by reciprocating it between not only various metal layers (e.g., signal lines) of the display panel and the backlight unit but also through interposed optical processing layers (e.g., polarizing sheets etc.), much of it may be lost when trying to get through the optical processing layers in the reuse round and it is therefore not efficaciously transmitted back through the display panel for forming a desired image.
As an example of a transmissive and actively illuminated thin panel display, the liquid crystal display (LCD) is that is now widely used and it typically has two spaced apart panels in which respective, electric field generating electrodes are placed, such as pixel electrodes and counterfacing parts of a common electrode. A liquid crystal material layer is interposed between the spaced apart panels. In the liquid crystal display, a voltage is applied to the field generating electrodes to generate an electric field extending into or through the liquid crystal layer. The generated electric field determines the direction of liquid crystal molecules of the liquid crystal layer, and an image is displayed by controlling the polarization of incident light.
The liquid crystal display typically includes at least one polarizer for polarizing the light from the backlight unit before such light enters the LCD panel. The polarizer may be attached to the outside of the LCD panel. In the case of a display device including the polarizer, since light incident inside the display panel is once-polarized light, if that light is reflected from the lower surfaces of the various metal layers inside the display panel back to the backlight unit, the polarization state of the light is changed by the reflection process, and the light with the modified polarization is again passed through the polarizer and its transmittance through the polarizer is decrease due to the reflection-induced change in polarization. Whatever once-reflected light does get through, that light has its polarization state changed by the reflection process in the backlighting unit before it comes back to the backside polarizer of the display panel. In other words, because the above-described process is serially repeated, light efficiency for back-reflected light may substantially drop to effectively become about 0.
It is to be understood that this background of the technology section is intended to provide useful background for understanding the here disclosed technology and as such, the technology background section may include ideas, concepts or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to corresponding invention dates of subject matter disclosed herein.